Abstract
The JMH blood group system consists of six high-prevalence antigens. These antigens are located on the Sema7A protein. The molecular basis of the JMH1– phenotype is not known; however, single nucleotide changes in the SEMA7A gene on chromosome 15 account for the other JMH antigens. JMH1, commonly known as JMH, is most notable because transient depression of the antigen occurs and anti-JMH may develop. These antibodies are most commonly observed and are not significant in transfusion. Antibodies developed in the rare JMH variant types may cause reduced red cell survival. This review provides a general overview of the JMH blood group system, including the serologic and molecular characteristics as well as proposed functions of the Sema7A protein. Immunohematology2014;30:18–23.